Vitreous enameling process



Dec. '7, 1937. H, F G|LBERT 2,101,616

vVITREOUS ENAMELING PROCESS Original Filed Aug. 3, 1933 Patented Dec. 7,1937 PATENT OFFICE VITREOUS ENAMELING PROCESS Herman F. Gilbert,Greenville, Mich., signor to Gibson Electric Refrigerator Corporation, acorporation of Michigan Substitute for application Serial No. l683,457,August 3, 1933. This application February Z3, 1937, Serial N0. 127,284

^ 4 Claims.

This invention relates to porcelain enamel processes, and isparticularly directed to overcoming certain dimculties which have inpastpracticed methods of applying such enamels prevented attainmentofuniform results, and frequently caused spoilage of large quantities ofwork. Avoidance of such spoilage in processes involving the applicationof vitreous enamels by dipping was regarded as unavoidable, inasmuch asits causes were unknown.

In some enameling plants these diiliculties seemed to vary with theseasons and weather, and' in some plants also they were more seriousthan in others. In many enamellng establishments it was found, forexample, that at timesI perfect work could be turned out consistentlyand over considerable periods, while at other times, or after a suddenand inexplicable, apparently causeless change, without variance by thepersons in charge of the process or materials used, the frit would tendto 'separate from the setting up agents in the enamel too quickly, andthe resultant work would become too thin in some areas and too thick inothers, rough and orange peeled. Frequently such enamel was then thrownaway, which is of course wasteful and expensive, or additionalsetting-up agent was added to lthe mixture. The latter expedient is avery poor and hazardous practice, however, asideirom introducingadditional expense and delay. `In any event, redraining of the imperfectwork was frequently necessitated, causing further delay and expense, orthe work was delivered imperfect, or scrapped or sold a't a lowpricebecause of the defective finish. Such elements of uncertainty and waste,heretofore regarded as unavoidable in the art, it is the primary objectof this invention to overcome.

Other objects and advantages will be apparent from the followingdescription, wherein reference is made to the accompanying drawingillustrating a preferred embodiment of my invention and wherein similarreference numerals designate similar parts in the drawing.

The single gure of drawing shows in perspective and partly broken away awaterjacketed dip tank constituting asuitable receptacle for and meansfor controlling the temperature of the enamel.

In carrying out my improved process the general4 order of procedure nowin use may be iollowed insofar as the sequence and nature of the severalsteps are concerned. I introduce as an additional element, however, acontinuous and (Cl. Sil-72) careful control of the temperature of theenamel throughout the entire period of its use.

Ordinarily the enamel is first ground with water in a pebble mill or thelike, and its consistency and color modied by the addition of 5 clay,borax or other setting-up agents, and a suitable oxide pigment, to theconstituents of the enamel itself, commonly termed frit, which maycomprise such substances as silica, feldspar, magnesia, quartz, sand andcobalt, although these l0 are merely exemplary and other materials maybe used. The milling operation heats the mixture considerably, and theheat in turn has the effect of thickening the enamel. Immediately after`milling, the complete enamel, comprising the 15 frit, setting-up andopacifying agents, would accordingly be too thick to be used without theaddition of water, while if water were to'be added at that time toreduce it to the proper'consistency, it would become too thin uponcooling, as 20 a result of which the coating which adhered to the waredipped therein would also be too thin. The milling also charges theenamel with considerable air. As a result of these considerations it isthe practice to allow the enamel to age 25 from twenty-four toforty-eight hours after milling, during which time the air escapes andthe enamel cools to a point where its consistency is suitable to permitit to be worked with.

I have found, however, that after the aging s0 process is completed andthe enamel has once cooled, an increase in temperature has a reverseeffect, and results in thinning the enamel, causing the frit particlesand setting-up agents to separate prematurely, thus weakening itssuspending strength and allowing the enamel to slip too freely, andmaking the coating which adheres to articles dipped therein much toothin and very irregular. This effect is seen4 also in a tendency of theenamel to Wash itself off the ware as it drains downward therefrom,leaving the coating uneven from top to bottom as Well as rough andorange peeled by reason of the weakening of the floating agentia,A Ihave further found thatany temperature materially over seventy degreesFahrenheit is sumcient to produce this highly yundesirable effect,` uponvthe enamel after its aging is once completed. Thus as it cools downduring the aging process after milling, no matter what the temperaturemay be inthe plant or other establishment where the work is beingdoneeven though the air temperature may be over eighty, asit frequentlyis-the enamel will inevitably at some time reach the proper consistency.It is this fact which has doubtless misled prior workers in the art, forif the temperature is too high, that proper consistency cannot long bemaintained, and the enamel particles begin to separate and the mixtureto thin in the well known and objectionable manner above referredto,-because of the aforementioned reverse eiect of heat after the agingprocess is complete. If after aging, however, the temperature of theenamel is controlled and prevented from rising above approximatelyseventy degrees, being preferably prevented from fluctuating more than afew degrees and held at a temperature between sixty-five and seventydegrees, it will maintain its specific gravity indefinitely withouttending to separate and thin out. It thus becomes possible to set up theconstituents in the mill studiedly, and with the knowledge that thefinished enamel can be held at the calculated specific gravity; and thecoating which adheres to ware dipped in enamel whose temperature hasbeen so controlled is remarkably smooth and uniform. Spoilage because offailure of the enamel itself becomes literally unknown, and after thesubsequent drying and firing operations perfect finish is invariablysecured. 'I'he temperature of the enamel can be allowed to rise as highas 85 F. and fluctuation only restricted against variations of more thantwenty or twenty-five degrees, and such control will have beneficialresults, although the specic gravity of the mix cannot be maintained aswell or as permanently in such manner as if the preferred temperaturespreviously noted are held.

Inasmuch as in most enameling plants tanks are used for holding theenamel in which the ware is dipped, and as the temperatures in theplants themselves fluctuate widely, not only because of climaticconditions but because of the proximity, of firing furnaces and otherapparatus and machinery, it is necessary in order to attain thedisclosed advantages of temperature control of the enamel, to providepractically constant temperature controlling means. I have found that avery satisfactory method of holding the temperature of the enamel withinthe desired limits is to provide the dip tank with a water jacket,connected to a source of water supply whose temperature is held withinthe desired limits. Other temperature controlling agents may of coursebe used, the important` consideration being, as above stated, the properi control of the temperature of the enamel in the disclosed manner.

As shown in the drawing, a suitable watercooled dip tank may compriseinner and outer box-like receptacles, designated I, 2 respectively,between which sealed water Jacket space 3 is left. lA water inlet 4 isprovided near the top of the tank upon one side, opening into the jacketspace, and a similarly connected outlet 5 upon the other. The inlet maybe connected to a suitable supply of water at proper temperature (notshown) and the outlet run to a drain or applied to any suitable use. Adrain 6 for the enamel is sealed in the inner receptacle and extendsthrough the jacket to permit drawing olf the enamel when desired, andthe tank assembly may if desired be mounted on a suitable support las 1.

By controlling the temperature of the enamel in the disclosed or othersuitable manner during the stated portions of the enameling process, andpreferably within the specified limits, the percentage of perfect workwhich may be turned out uninterruptedly with a single outlay ofenameling equipment is greatly increased, and losses because of thepreviously uncontrollable failures of the enamel, which developedheretofore with costly frequency, are completely eliminated.

While it will be apparent that the illustrated embodiment of myinvention herein disclosed is well calculated to adequately fulill theobjects and advantages primarily stated, it is to be understood that theinvention is susceptible to variation, modification and change withinthe spirit and scope of the subjoined claims.

This application is a substitute for application Ser. No. 683,457, filedAugust 3, 1933.

I claim:

1. '111e process of vitreous enameling which comprises milling a mass ofenamel frit, opacifying agent, setting up agent and water, whereby themass becomes heated and aerated, aging the resulting mixture for anextended period to cool the same and remove air, thus producing anenamel slip of a predetermined viscosity, dipping articles to be coatedinto the slip, the temperature of the slip being directly controlledthroughout the active life thereof to prevent a temperature change afterthe completion of the aging operation of more than 25 F., andmaintaining the temperature thereof after aging below a maximum of 85 F.whereby the predetermined viscosity is maintained substantiallyconstant.

2. 'I'he process as set forth in claim 1, in which the mass ismaintained in an enclosed zone during the dipping operation, and a fluidis mechanically circulated about said zone to maintain the specifiedtemperature of the mass.

3. The process of vitreous enameling which comprises milling a mass ofenamel frit, opacifying agent, setting up agent and water,wh erebythemass becomes heated and aerated, aging the resulting mixture for anextended period to cool the same and remove air, thus producing anenamel slip of a predetermined viscosity, dipping articles to be coatedinto the slip, the temperature of the slip being directly controlled bya mechanically circulated liq'uid throughout the active life thereof toprevent a temperature change after the completion of the aging operationof more than 25 F., whereby the predetermined viscosity is maintainedsubstantially constant.

4. The process of vitreous enameling which comprises milling a mass ofenamel frit, opacifying agent, setting up agent and water, whereby themass becomes heated and aerated, aging the resulting mixture for anextended period to cool the same and remove air, thus producing anenamel slip of a predetermined viscosity, dipping articles to be coatedinto the slip, the temperature of the slip being directly controlledthroughout the active life thereof to prevent a temperature change afterthev completion of the aging operation of more than 10 F., andmaintaining the temperature thereof after aging below a maximum of 75F., whereby the predetermined viscosity is maintained substantiallyconstant.

HERMAN F. GnriBEaT.

